1. Field of the Invention
The present invention relates to man-machine compatibility with respect to closed-loop control of vehicles. Specifically, the present invention relates to tactile feedback systems. More specifically, the present invention relates to an improved and intuitive tactile feedback to the vehicle operator on the status of the vehicle's controls that counters the current trend of utilizing control-by-wire and or power controls that greatly reduce the operator's “feel” for the limitations imposed on the control system by failures, configuration idiosyncrasies, seldom encountered and unanticipated operating conditions, and design limitations that can result in catastrophic loss of vehicle control.
2. Description of the Related Art
Many vehicle control systems use hydraulic, mechanical, or electrical power to augment the operator's control forces to reduce the operator's workload for maneuvering the vehicle. But the more work done by the power system, the less tactile information is being transmitted back through the inceptor to the operator on the status of the control system. For example, the operator will not detect the increase in control forces on a system in need of lubrication as readily because the power system is providing much of the additional force required. For large vehicles, such as commercial aircraft, there is further masking of information by the system compliance, the stretching of cables, the bending of the mounting brackets and push rods, and the over-travel springs on the actuator servo valves.
The latest advance in vehicle control technology to be widely implemented is the control-by-wire, which replaces the force transmitting mechanical linkage between the inceptor and the effector with a wire transmitting the inceptor generated electric signal commanding the effectors to action. A multitude of benefits are attributed to the adoption of control-by-wire technology, but the compromise was the acceptance that tactile feel for the status of the flight control system were either not needed, or could be provided through alternate sensory channels. One of the unanticipated consequences of replacing the mechanical linkage with wire, was the resulting incidences of operators, when unexpectedly encountering a life threatening situation, responding by moving their inceptors at such a rate that the effectors could not keep up, markedly increasing the phase delay between the inceptor input and the associated effector output. Phase delay is a key factor in the experiencing of loss of control associated with the aircraft-pilot or operator-vehicle coupling phenomena.
Loss of control from aircraft-pilot coupling is the result of the pilot trying aggressively to help the aircraft either recover from an upset, or to acquire a new flight path because of an impending threat on the original course. Under such circumstances, the pilot will choose to act like an additional stability augmentation system in order to more responsively acquire the desired flight path, and quickly dampen any overshoots resulting from the recovery maneuver. The consequences of the phase delay are that while the pilot's inceptor inputs are trying to enhance the stability, the resulting effector output may be doing just the opposite because of the phase delay.
The invention fills the void created by the adoption of control-by-wire technology in tactile feedback through the inceptor to the vehicle operator on the status of the critical functions of the vehicle control system.
“Loss of Control” was the single largest fatal accident category for the worldwide commercial jet fleet from 1994 through 2003, and has consistently been either the first or second largest fatal accident category since the beginning of accident data collection. Specific factors that cause loss of control are many and varied, but a common indicator for several recent aircraft accidents has been the lack of awareness by the pilot of anomalous behavior of the flight control system, caused by a control surface not following the pilot's commands to the level of accuracy needed to maintain control of the aircraft.
With the degree of technical sophistication involved in assuring that today's aircraft are easily controllable, with redundancy providing fail-safe operations even after one or two failures of key components, there continues to be room for improvement. Recent advances in flight control designs, such as fly-by-wire, have eliminated the pilot's tactile feel for a jammed or frozen control surface, or for hitting the control surface deflection stop. Generally, there is little or no restraining force on the cockpit inceptors to alert the pilot for exceeding the control surface rate limits. Such tactile feedback, which was an implicit pilot cue in early aircraft, is substantially eroded with the introduction of the fully powered hydro-mechanical control systems, and completely eliminated with the introduction of fly-by-wire control systems.
Other vehicle types are adapting control systems that utilize control-by-wire technology. The control-by-wire (CBW) control systems, when used as part of the vehicle's primary maneuver controls, are subject to the same challenges that have been experienced in air vehicles. For example, the loss of tactile feedback to the operator on deteriorating conditions of the control system and the anticipated vehicle response, which can lead to loss of control unless appropriately compensated for by the operator.
An approach to addressing the problems noted above is to provide the vehicle operator with tactile feedback on deteriorating conditions with the vehicle controls. Specifically, one way this can be accomplished is by providing increasing resistance to the inceptor proportional to the severity of the deterioration, the vehicle operator will initially be alerted by the increased resistance felt during control application, with the resistance ultimately increasing to thereby maintain safe control of the vehicle.
There have been attempts to address the problems noted above. For example, U.S. Pat. No. 6,339,419, issued to Jolly et al., refers to a magnetically controllable system. In Jolly '419, a haptic interface system using force feedback and a magnetically-controllable device that provides resistance forces opposing joystick movement is disclosed. The system includes a computer system that runs a program similar to a computer game that can use a joystick which is similar to that which is used in an aircraft. The joystick is in contact with a pilot or an operator and the haptic interface device which is in contact with the controller provides resistance to the operator's motion. The computer system provides a variable output signal corresponding to a feedback force and the magnetically controllable device varies the feedback force based on the output signal. The feedback force is varied by changing the density of the magnetically controlled fluid in response to the output signal. Similarly, U.S. Pat. No. 6,373,465, issued to Jolly et al., discloses a magnetically controllable device adapted for use in a feedback computer system to provide force feedback sensations to the system's operator. The system in Jolly '465 includes a computer system that runs a program which controls a haptic interface device, similar to a joystick in an aircraft.
U.S. Pat. No. 6,283,859, issued to Carlson et al., discloses a feedback system using a magnetically controllable haptic interface system wherein a magnetically controllable fluid is employed in the device. Carlson '859 is directed to providing computer game operators with “feel sensations” so they can get a realistic simulation of the computerized game. According to Carlson, a variable resistance force in proportion to the strength of an applied magnetic field is provided.
U.S. Pat. No. 5,062,594, issued to Repperger, discloses a flight control system with tactile feedback. In Repperger '594 there is a roll system which has visual feedback and includes a feedback system which provides feel derived from signal sources. Repperger '594 uses an algorithm which is characterized mathematically. The control system in Repperger '594 is a passive control system, wherein feedback forces are based on the pilot input to the flight control system.
Lastly, U.S. Pat. No. 4,599,070, issued to Hladky et al., discloses a method and system apparatus for simulating a control system, such as an aircraft control system. According to Hladky '070 a moveable control is simulated in which force and movement parameters of the control can be varied in accordance with simulated operation of the system. Feedback feel is accomplished through the use of levers having an adjustable fulcrum. The control system in Hladky '070 is a programmed passive system, wherein forces are simulated based on the programmed set of simulated conditions.
There remains a need for a tactile feedback system that can alert the operator, through tactile feedback generated by increasing the friction force on the inceptor as a function of the severity of potential loss of control conditions. Furthermore, there remains a need for a tactile feedback system that can produce a restraining force to counter operator vehicle coupling loss of control conditions. Thus, it would be advantageous to provide an improved tactile feedback system that can alert the operator, through tactile feedback generated by increasing the friction force on the inceptor as a function of the severity of potential loss of control conditions. It would also be advantageous to provide an improved tactile feedback system that can produce a retaining force to counter operator vehicle coupling loss of control conditions.